We propose to develop and use a technique for estimating the timing of the opening of acetyl-choline channels at the neuromuscular junction of the frog. We will use this technique to study the pattern of channel opening during a normal min. e.p.p.; the change in timing of channel opening produced by poisoning the acetylcholinesterase and the pattern of channel opening during end-plate potentials, with emphasis on the effects of facilitation. We also will study the effects of temperature during a recovery period following tetanic stimulation on quantal size. Preliminary evidence suggest that low temperatures lead to large quanta, while high temperatures lead to small quanta. We hope that this line of investigation will lead to a better understanding of the factors responsible for quantal size.